OBD-II TROUBLE CODE GUIDE
P0128: Coolant Thermostat Below Regulating Temperature
The engine is taking longer than expected to reach normal operating temperature.
What P0128 means
The engine is taking longer than expected to reach normal operating temperature.
Common possible causes
- Thermostat stuck open
- Low coolant level
- Temperature sensor or cooling-fan problem
What to check first
Record all stored and pending codes and freeze-frame data before clearing anything. Inspect relevant wiring, connectors, hoses, fluid levels, and obvious damage. Use vehicle-specific service information and test the affected system before purchasing parts.
A code is not a parts order. Several faults can create the same code, and replacing the component named in a code description may not correct the underlying problem.
Look up P0128 for my vehicle